Descriptive Studies Person Place and Time Descriptive Epidemiology

Descriptive Studies: Person, Place and Time

Descriptive Epidemiology • Includes activities related to characterizing the distribution of diseases within a population Analytical Epidemiology • Concerns activities related to identifying possible causes for the occurrence of diseases

Descriptive Epidemiology • Epidemiological equivalent of the game “ 20 Questions” ü animal, mineral or vegetable? • In Descriptive Epidemiology: ü Who? - person ü Where? - place ü When? - time

Descriptive Epidemiology PLACE TIME PERSON Think of this as the standard dimensions used to track the occurrence of a disease.

Person • WHO is getting the disease? • Many variables are involved and studied, but factors such as sex, age & race often have a major effect.

Characteristics of Person • • Age Sex Ethnic group Socioeconomic status Nativity Religion Marital status Occupation

Age

Age

Sex

Time • WHEN does the disease occur? ü“Temporal” üRange from hours to decades • Type of disease dictates “time” element to be used • Graphic format often used ü y-axis (vertical) - frequency ü x-axis (horizontal) - time

Characteristics Relating to Time • • Secular change (long-term) Point epidemics (short-term) Cyclic trends Seasonal variation

Secular Change

Secular Change • Secular changes (“temporal variation”) occur slowly over long periods of time ü Longer than one year Incidence Rates of Cancers in Women Incidence Rates of Cancers in Men

Point Epidemics • Short-term changes occur over limited time frames ü Hours ü Days ü Weeks ü Months • Used for short-term exposures or diseases with short incubation and/or illness durations

Point Epidemics

Point Epidemics

Cyclic Trends • Cyclic trends may be either long-term or short term events. • Some are “seasonal” while others are cyclic due to other factors: ü Immigration ü School year ü Military deployment

Cyclic Trends

Seasonal Variation • Seasonal variation can be seen for some diseases or conditions falling within a calendar year

Seasonal Variation • Seasonal variation can be used to suggest possible etiology. Migratory Birds?

Time Clustering • Time clustering data can sometimes be used to trace the “beginning” to the introduction of a specific causal agent ü Thalidomide & birth defects First marketed in Europe in 1950’s as sleeping pill and to treat morning sickness in pregnant women ü Toxic Shock Syndrome Staphylococcus aureus infection in women using newly introduced hyperabsorbent tampons

Time Clustering

Place • WHERE are the rates higher? lower? • Geographic location of source • Geographic location of reservoir

John Snow and Cholera

5 Criteria of Place • Rate observed in all ethnic groups in the area • Rate NOT observed in persons of similar groups inhabiting other areas • Healthy persons entering area get ill at same frequency • People who leave do NOT show similar levels • Similar levels of infestation in other species (if zoonotic disease)

Characteristics Relating to Place • International • Variation within countries ü Urban-rural ü Local • Building Maps

Place Distribution of AIDS in the US 1990

Local

Building Maps

Interactions of Time and Place • Time-place clustering • Migration